The development of silver halide photographic materials involved a long-series of struggles seeking methods by which increases in photographic speed could be achieved and deteriorations in graininess and developed image sharpness, which tend to increase with increasing photographic speed, could be suppressed to the minimum.
In general, high photographic speed can be attained by increasing the size of the silver halide grains used. Such is, however, well known to cause a deterioration of the image produced in graininess and sharpness.
Conversely, decreasing the size of silver halide grains is known to bring about an improvement in graininess. However, it is also well known that a decrease in grain size reduces photographic speed.
A large number of means for increasing the photographic speed of silver halide grains as their size remains relatively small have been investigated. For instance, an attempt to increase photographic speed by increasing the iodide content in the halide composition of silver halide grains was made. However, this proved to be not so successful.
On the other hand, there are known methods of improving graininess through the inhibition of development where triazoles or tetrazoles are incorporated as development inhibitor into a light-sensitive material.
However, such development inhibitors restrain development uniformly, regardless of the image density to be developed. Accordingly, they do not necessarily have satisfactory effects upon improving the graininess and sharpness of developed image.
Consequently, it has been highly desired to develop a means which makes it feasible to allow development inhibition to proceed in proportion to the density to be developed, that is, whereby development in an image area can be retarded to a greater extent the higher the density to be developed therein is, whereby a remarkable improvement in graininess and sharpness can be achieved.